A multilayer ceramic capacitor, which is a primary application of the present invention, is generally manufactured as described below.
First, ceramic green sheets are prepared which include a dielectric ceramic raw material and whose surfaces are provided with a conductive material to be formed into internal electrodes each having a desired pattern. As the dielectric ceramic, for example, a dielectric ceramic including a BaTiO3-based compound as a primary component may be used.
Next, a plurality of ceramic green sheets including the above-described ceramic green sheets each provided with the conductive material are laminated to each other and are thermal-bonded, so that an integrated green laminate is formed.
Subsequently, by firing this green laminate, a sintered ceramic laminate is obtained. Inside this ceramic laminate, internal electrodes composed of the above-described conductive material have been formed.
Next, external electrodes are formed on outer surfaces of the ceramic laminate so as to be electrically connected to the respective internal electrodes. The external electrodes are formed, for example, by applying a conductive paste including a conductive metal powder and a glass frit to the outer surfaces of the laminate, followed by firing. By the process described above, a multilayer ceramic capacitor is formed.
As a dielectric ceramic suitable for a multilayer ceramic capacitor, for example, a barium titanium-based ceramic (BaTiO3) may be mentioned. For example, in Japanese Unexamined Patent Application Publication No. 03-040962 (hereinafter referred to as “Patent Document 1”), a dielectric ceramic including barium titanate as a primary component and SnO2, Bi2O3, MgO, SiO2, La2O3, Sm2O3, and Nd2O3 as accessory components has been disclosed.
However, since the dielectric ceramic disclosed in Patent Document 1 has a low Curie temperature of −20 to 15° C., the dielectric constant thereof rapidly increases as the temperature increases, and there has been a problem in that the above dielectric ceramic cannot be used in a high temperature region. In particular, since a multilayer ceramic capacitor have been recently used for automobile applications, it is desired that the multilayer ceramic capacitor be stably useable at a high temperature of approximately 175° C. Accordingly, the Curie temperature is preferably at least 130° C. or more.
Accordingly, a dielectric ceramic composition has been disclosed in International Publication WO 2005/075377 Pamphlet (hereinafter referred to as “Patent Document 2”) which includes a perovskite type compound represented by the composition formula: (Ba,Sn)TiO3 as a primary component and which has a Curie temperature of 130° C. or more.
In the dielectric ceramic composition disclosed in Patent Document 2, the Curie temperature of the ceramic is increased to 130° C. or more since Sn is located in the Ba site as a divalent cationic element.
In general, Sn is usually located in the Ti site in a barium titanate-based ceramic since tetravalent cationic Sn is placed in a stable state. When the Ti of barium titanate is replaced with Sn, as disclosed by K. Okazaki, “Ceramic Dielectric Technologies” 3rd edition, pp. 281 to 283, published by Gakken-sha (hereinafter referred to as “Non-Patent Document 1”), the Curie temperature of 120° C., which is obtained when Ti is not replaced with Sn, considerably decreases to room temperature or less. The reason the dielectric ceramic disclosed in Patent Document 1 has a low Curie temperature is also believed that Sn is located in the Ti site as a tetravalent cationic element.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 3-040962
Patent Document 2: International Publication WO 2005/075377 Pamphlet
Non-Patent document 1: K. Okazaki, “Ceramic Dielectric Technologies” 3rd edition, pp. 281 to 283, published by Gakken-sha